1. Field of the Invention
The present invention relates to a primer composition which has excellent adhesive properties. More specifically, it relates to a primer composition suited to adhering silicone rubber of the heat-curing type, particularly fluorosilicone rubber, to various types of substrates, such as metal surfaces.
2. Description of the Prior Art
Fan and Show in Japanese Patent Publication No. Sho 49[1974]-5730 have described using vinyl-tris(tert-butylperoxy)silane as a primer for adhering EPDM, EPR, chlorinated polyethylene, or silicone rubber to surfaces of glass and metal. However, this primer exhibits drawbacks such as the necessity of long-term heat treatment at an elevated temperature and pressure. For this reason, Maizumi and Inoue in Japanese Patent No. Sho 50[1975]-35,530, published Nov. 17, 1975, describes an adhesive primer composition which can be used as a primer for attaching thermoplastic resins to each other or attaching thermoplastic resin to glass, metals, or metal oxides at low temperatures in a short period of time. The primer composition of Maizumi and Inoue is composed of vinyltris(tertiary-butylperoxy)silane, an organoperoxide whose half-life is 1 minute at 130.degree.-190.degree. C., and an inert organic solvent. However, this primer composition of Maizumi and Inoue exhibits slow air-drying and slow thermosetting properties after it has been coated over with a material to be attached. Therefore, the primer layer coated on the material surface moves from one location to another location by press insertion of material during injection- or press-molding processes. For this reason, this primer composition of Maizume and Inoue exhibits not only drawbacks such as difficulty in achieving uniform adhesion, but also the drawback of interfacial delamination which can be detected by inspection of the adhesion properties of silicone rubber, especially fluorosilicone rubber as a material to be attached. For this reason, this primer composition of Maizumi and Inoue is unsatisfactory for attaching silicone rubber to a substrate, especially for attaching fluorosilicone rubber to a substrate.
As a result of extensive investigations to improve the above-mentioned drawbacks, the present inventors were able to perfect a primer composition which air dries and cures well, with which an adhesion effect is obtained by thermocompression bonding at comparatively low temperatures and in a short period of time, and which is effective in adhering silicone rubber to a substrate, particularly in adhering fluorosilicone rubber to a substrate. We discovered, as described in our copending application Ser. No. 308,335, filed Oct. 5, 1981, entitled "An Adhesive Primer Composition," that using a primer composition comprising a mixture of an organosilicon compound having at least one alkoxy or alkoxyalkoxy radical per molecule, vinyltris(tertiary-butylperoxy)silane, and organic solvent was an excellent primer which overcame the drawbacks. We have now made a further discovery which allows up to make a primer composition, equally as good as our primer composition described in Ser. No. 308,335, without having to make the vinyltris(tertiary-butylperoxy)silane and therefore a less expensive primer composition is obtained.